The 41-year-old from Herringswell, Suffolk, pleaded guilty to 25 offences including sexual assault and the making of more than 16,000 indecent images.

He was bailed and is due to be sentenced at a later date.

As he left court, Bradbury told reporters "I'm so sorry" and refused to answer further questions.

The offences involved 18 complainants, prosecutor John Farmer said.

The court heard the blood cancer specialist had worked at the hospital for five years.

'Sexual gratification'

He was suspended after a complaint about his behaviour in November last year.

The hospital said it was "sickened" by the abuse

A spokesman for Addenbrooke's Hospital said Bradbury no longer worked for Cambridgeshire University Hospitals Trust.

In total he pleaded guilty to six counts of sexual assault and 13 counts of engaging in sexual activity with a child.

Bradbury also admitted three counts of causing or inciting a child to engage in sexual activity, one count of voyeurism and two counts of making indecent images of a child.

He pleaded not guilty to a count of sexual activity with a child and a count of sexual assault, which Judge Gareth Hawkesworth said would likely remain on file.

'Vulnerable victims'

The judge said the doctor could expect a "substantial" custodial sentence and would have to sign the sex offenders register.

Addenbrooke's Hospital said it had set up ahelpline for anyone affected by the case.

Dr Keith McNeil, its chief executive, said: "Our most abject and sincere apologies go out to any and all of our patients and their families who are affected by this in any way.

"There is a very ancient and sacred trust that exists between a doctor and his patients, and quite frankly, it sickens me to think that trust has been breached."

Chief nurse Ann-Marie Ingle, said: "His cold and calculating abuse of trust has deeply shocked us all, including staff who worked alongside him to care for these vulnerable and sick children.

"As soon as we were alerted, we took immediate action to suspend him from clinical practice."

Det Sgt Shane Fasey, of Cambridgeshire Police, said: "Bradbury's offences were an appalling breach of trust committed against vulnerable victims who had been placed in his care.

"The families believed the boys were in his safe hands but they were actually being abused by Bradbury, who carried out examinations purely for his own sexual gratification and with no medical justification whatsoever."